Institute of Earth Environment
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PM2.5 composition and sources in the San Joaquin Valley of California: A long-term study using ToF-ACSM with the capture vaporizer
No full textThe San Joaquin Valley (SJV) of California has suffered persistent particulate matter (PM) pollution despite many years of control efforts. To further understand the chemical drivers of this problem and to support the development of State Implementation Plan for PM, a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) outfitted with a PM2.5 lens and a capture vaporizer has been deployed at the Fresno-Garland air monitoring site of the California Air Resource Board (CARB) since Oct. 2018. The instrument measured non-refractory species in PM2.5 continuously at 10-min resolution. In this study, the data acquired from Oct. 2018 to May 2019 were analyzed to investigate the chemical characteristics, sources and atmospheric processes of PM2.5 in the SJV. Comparisons of the ToF-ACSM measurement with various co-located aerosol instruments show good agreements. The inter-comparisons indicated that PM2.5 in Fresno was dominated by submicron particles during the winter whereas refractory species accounted for a major fraction of PM2.5 mass during the autumn associated with elevated PM10 loadings. A rolling window positive matrix factorization analysis was applied to the organic aerosol (OA) mass spectra using the Multilinear Engine (ME-2) algorithm. Three distinct OA sources were identified, including vehicle emissions, local and regional biomass burning, and formation of oxygenated species. There were significant seasonal variations in PM2.5 composition and sources. During the winter, residential wood burning and oxidation of nitrogen oxides were major contributors to the occurrence of haze episodes with PM2.5 dominated by biomass burning OA and nitrate. In autumn, agricultural activities and wildfires were found to be the main cause of PM pollution. PM2.5 concentrations decreased significantly after spring and were dominated by oxygenated OA during March to May. Our results highlight the importance of using seasonally dependent control strategies to mitigate PM pollution in the SJV
FeCo alloy encased in nitrogen-doped carbon for efficient formaldehyde removal: Preparation, electronic structure, and d-band center tailoring
No full textFormaldehyde is a typical indoor air pollutant that has posed severely adverse effects on human health. Herein, a novel FeCo alloy nanoparticle-embedded nitrogen-doped carbon (FeCo@NC) was synthesized with the aim of tailoring the transition-metal d-band structure toward an improved formaldehyde oxidation activity for the first time. A unique core@shell metal-organic frameworks (MOFs) architecture with a Fe-based Prussian blue analogue core and Co-containing zeolite imidazole framework shell was firstly fabricated. Then, Fe and Co ion alloying was readily achieved owing to the inherent MOF porosity and interionic nonequilibrium diffusion occurring during pyrolysis. High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectra confirm that small FeCo alloys in situ form in FeCo@NC, which exhibits a higher formaldehyde removal efficiency (93%) than the monometallic Fe-based catalyst and a remarkable CO2 selectivity (85%) at room temperature. Density functional theory calculations indicate the number of electrons transferred from the metal core to the outer carbon layer is altered by alloying Fe and Co. More importantly, a downshift in the d-band center relative to the Fermi level occurs from - 0.93 to - 1.04 eV after introducing Co, which could alleviate the adsorption of reaction intermediates and greatly improve the catalytic performance
Experimental-computational approach for elucidating the dissolution behavior of potassium phosphates in near- and supercritical water
No full textThe present work investigates the solubility of dipotassium and monopotassium phosphate in near- and supercritical water. The highest solubilities exceeded 100 mmol kg(-1) at 633.15 K and 30 MPa, the lowest temperature and highest pressure conditions examined, while at 723.15 K and 19 MPa, the lowest solubilities were observed for approximately 0.2 mmol kg(-1) and 0.001 mmol kg(-1). For potassium phosphates, increasing density and decreasing temperature monotonically increased their solubility. Three semi-empirical models were employed to correlate the measured solubility data. Enthalpy model and ionization model were demonstrated to provide the highest accuracies for correlating the experimental solubility of di- and monopotassium phosphate, respectively. The chemical equilibrium reactions facilitating the dissolution and precipitation of potassium phosphates were assessed by theoretical calculations via R-HKF equations of state. Calculations by the R-HKF EOS indicated that precipitation was thermodynamically favored under all conditions, however, increasing temperature and water density promoted the dissolution and hydrolysis of potassium phosphates
Experimental-computational approach for elucidating the dissolution behavior of potassium phosphates in near- and supercritical water
No full textThe present work investigates the solubility of dipotassium and monopotassium phosphate in near- and supercritical water. The highest solubilities exceeded 100 mmol kg(-1) at 633.15 K and 30 MPa, the lowest temperature and highest pressure conditions examined, while at 723.15 K and 19 MPa, the lowest solubilities were observed for approximately 0.2 mmol kg(-1) and 0.001 mmol kg(-1). For potassium phosphates, increasing density and decreasing temperature monotonically increased their solubility. Three semi-empirical models were employed to correlate the measured solubility data. Enthalpy model and ionization model were demonstrated to provide the highest accuracies for correlating the experimental solubility of di- and monopotassium phosphate, respectively. The chemical equilibrium reactions facilitating the dissolution and precipitation of potassium phosphates were assessed by theoretical calculations via R-HKF equations of state. Calculations by the R-HKF EOS indicated that precipitation was thermodynamically favored under all conditions, however, increasing temperature and water density promoted the dissolution and hydrolysis of potassium phosphates
Inflammatory and oxidative stress responses of healthy elders to solar-assisted large-scale cleaning system (SALSCS) and changes in ambient air pollution: A quasi-interventional study in Xi'an, China
No full textAn outdoor solar assisted large-scale cleaning system (SALSCS) was constructed to mitigate the levels of fine particulate matter (PM2.5) in urban areas of Xi'an China, providing a quasi-experimental opportunity to examine the biologic responses to the changes in pollution level. We conducted this outdoor SALSCS based real-world quasiinterventional study to examine the associations of the SALSCS intervention and changes in air pollution levels with the biomarkers of systemic inflammation and oxidative stress in healthy elders. We measured the levels of 8-hydrox-2-deoxyguanosine (8-OHdG), Interlukin-6 (IL-6). as well as tumor necrosis factor alpha (TNF-alpha) from urine samples, and IL-6 from saliva samples of 123 healthy retired participants from interventional/control residential areas in two sampling campaigns. We collected daily 24-h PM2.5 samples in two residential areas during the study periods using mini-volume samplers. Data on PM10, gaseous pollutants and weather factors were collected from the nearest national air quality monitoring stations. We used linear mixed-effect models to examine the percent change in each biomarker associated with the SALSCS intervention and air pollution levels, after adjusting for time trend, seasonality, weather factors and personal characteristics. Results showed that the SALSCS intervention was significantly associated with decreases in the geometric mean of biomarkers by 47.6% (95% confidence interval: 16.5-67.2%) for 8-OHdG, 66% (31.0-83.3%) for TNF-alpha, 41.7% (0.2-65.9%) and 43.4% (13.6-62.9%) for urinary and salivary IL-6, respectively. An inter-quartile range increase of ambient PM 2 . 5 exposure averaged on the day of the collection of bio-samples and the day before (34.1 mu g/m(3)) was associated, albeit non-significantly so, with 22.8%-37.9% increases in the geometric mean of these biomarkers. This study demonstrated that the SALSCS intervention and decreased ambient air pollution exposure results in lower burden of systemic inflammation and oxidative stress in older adults. (C) 2021 Elsevier B.V. All rights reserved
Differential health and economic impacts from the COVID-19 lockdown between the developed and developing countries: Perspective on air pollution
No full textIt is enlightening to determine the discrepancies and potential reasons for the degree of impact from the COVID-19 control measures on air quality as well as the associated health and economic impacts. Analysis of air quality, socio-economic factors, and meteorological data from 447 cities in 46 countries indicated that the COVID-19 control measures had significant impacts on the PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 mu m) concentrations in 20 (reduced PM2.5 concentrations of -7.4-29.1 mu g m(-3)) of the selected 46 countries. In these 20 countries, the robustly distinguished changes in the PM2.5 concentrations caused by the control measures differed between the developed (95% confidence interval (CI): -2.7-5.5 mu g m(-3)) and developing countries (95% CI: 8.3-23.2 mu g m(-3)). As a result, the COVID-19 lockdown reduced death and hospital admissions change from the decreased PM2.5 concentrations by 7909 and 82,025 cases in the 12 developing countries, and by 78 and 1214 cases in the eight developed countries. The COVID-19 lockdown reduced the economic cost from the PM2.5 related health burden by 54.0 million dollars in the 12 developing countries and by 8.3 million dollars in the eight developed countries. The disparity was related to the different chemical compositions of PM2.5. In particular, the concentrations of primary PM2.5 (e.g., BC) in cities of developing countries were 3-45 times higher than those in developed countries, so the mass concentration of PM2.5 was more sensitive to the reduced local emissions in developing countries during the COVID-19 control period. The mass fractions of secondary PM2.5 in developed countries were generally higher than those in developing countries. As a result, these countries were more sensitive to the secondary atmospheric processing that may have been enhanced due to reduced local emissions
Quantifying the spatio-temporal variability of total water content in seasonally frozen soil using actively heated fiber Bragg grating sensing
No full textActively heated fiber-optic (AHFO) method has become a research focus for soil water content measurement in recent years due to its advantages such as small size, distributed measurement and good durability. However, the AHFO method is presently coupled to distributed temperature sensing (AHFO-DTS) which is inevitably limited by low temperature measurement accuracy and spatial resolution. Furthermore, the existing studies about AHFO method do not consider the existence of frozen soil caused by temperature changes, which further limits its application in the field. Here a new method for total water content measurement in frozen soil using actively heated fiber Bragg grating (AHFO-FBG) sensing is proposed for the first time, which directly determines the calibration formulas of frozen soil under different soil temperatures from the calibration formula of unfrozen soil. Moreover, the feasibility and reliability of AHFO-FBG technology are proved through laboratory calibration tests and in-situ monitoring data of Chinese loess, and the temporal and spatial distribution of total water content in shallow seasonally frozen loess is also revealed. It is suggested that the AHFO-FBG technology can complement with the traditional techniques to achieve quasi-distributed and in-situ total water content monitoring in seasonally frozen soil
Upward trend and formation of surface ozone in the Guanzhong Basin, Northwest China
No full textIncrease trend of surface ozone (O-3) was observed in the Guanzhong Basin (GZB) from 2014 to 2020 with growth rates of 3.9-6.4 mu g M-3 yr(-1) for the maximum daily average 8 h (MDA8) O-3 concentrations. To further understand the formation of O-3 , investigation of volatile organic compounds (VOCs) was carried out in the summer of 2018. High levels of VOCs were observed in both residential area and industrialized cities. Elevated concentrations of none-methane Hydrocarbon (NMHCs) were observed in rush hours, which indicated dominated roles of traffic activities on the loading of ambient VOCs. In the nighttime, both of NMHCs and oxygenated VOCs (OVOCs) were raised, and the peaks of VOCs kept pace with accumulation of O-3 . Wind field indicated that northward and westward air mass, which passed through the remote forest and industrial area in east of the GZB, was responsible to elevated ambient VOCs in the GZB. Traffic emission, fuel evaporation, and solvent using were key contributors to ambient NMHCs, while solvent using and secondary formation dominated the loading of OVOCs. The present study indicated that both local management and regional collaborative control on active VOCs species from typical sources is urgently needed in GZB
Novel methods of resolving daily growth patterns in giant clam (Tridacna spp.) shells
No full textSclerochronology is a powerful tool for high resolution paleoclimate and paleoenvironment reconstruction. However, we can only observe annual growth bands using traditional technology for most marine bivalves, hampering the ability to establish daily resolution chronology in order to reconstruct past weather changes. Giant clams (Tridacna spp.) are the largest bivalves in the world. Their hard and dense aragonite shells have clear annual and even daily growth bands, creating the potential for daily resolution chronology establishment and paleoweather reconstruction. In this study, we present two new and reliable methods that resolve daily growth patterns in giant clam shells: (1) Fluorescence image method. Measuring the width between two bright fluo-rescent bands of the Tridacna shell with the help of CooRecorder 9.0 software based on the clear daily growth bands obtained by laser scanning confocal microscope (LSCM). (2) Ultrahigh resolution Sr/Ca method. Counting the amount of Sr/Ca ratio data in each daily cycle derived from Tridacna shell, and then calculating the daily growth increment based on the spatial resolution of Sr/Ca data. The results show the variation of daily growth increments profiles obtained by the two methods synchronize, and the chronology uncertainty is statistically acceptable over a long-term record, indicating that both methods can estimate the daily growth increment of Tridacna shell reliably. The methods developed here lay the foundation for paleoweather reconstruction using daily growth increments of Tridacna spp
Unraveling the process of aerosols secondary formation and removal based on cosmogenic beryllium-7 and beryllium-10
No full textThe secondary formation and diffusion processes of aerosol are extraordinarily complex and significantly impact the environment and human health. Therefore, exploring the process of aerosol formation and diffusion based on independent new tracer has always been a concern. The Be-7 and Be-10, which are generated only by the action of cosmic rays, are chemically stable and adsorbed on aerosol for transmission, so they have the potential characteristics of aerosol tracers. Here, we obtained the daily resolution atmospheric Be-7, Be-10, and Be-10/Be-7 without dust interference in Xi'an autumn and winter (heavy pollution period in a typical polluted area) by accelerator mass spectrometry. It is found that during the rapid formation of secondary aerosols (SA) under the stable Be-10/Be-7 ratio, which indicates the stable atmospheric vertical structure, the concentration of Be-7 and Be-10 is significantly negatively correlated (R-2 > 0.9) with the aerosol concentration. Therefore, SA relative content in aerosols can be estimated by the dilution amount of Be-7 and Be-10 to reveal the secondary-formation process of aerosol (33% average contribution to aerosols during the winter heavy air pollution period). Furthermore, we also revealed the physical removal process of aerosols based on Be-7, Be-10, and Be-10/Be-7, including precipitation removal and diffusion of vertical atmospheric movement caused by stratospheric air intrusion. In summary, meteoric cosmogenic 7Be and 10Be will provide a new way to study the secondary chemical formation and physical removal of aerosols